题目内容
Greenhouse Effect
A greenhouse is a building made of glass which is used for keeping plants warm when the outside temperature is low. In a similar way, there are several gases in the atmosphere which trap the heat generated by the sun and prevent it from escaping. These gases are known as "greenhouse gases", and the way in which they trap heat in the atmosphere is called the "greenhouse effect". This is not simply air pollution like photochemical smog (光化学烟雾), for example. Most of the main greenhouse gases occur naturally in small amounts in our atmosphere, and without them the earth would be thirty degrees colder and human life would not exist. In other words, the greenhouse effect is a natural process which is to some extent beneficial to us.
The problem is that in the last century and a half, we have been putting excessive amounts of these gases into the earth's atmosphere by burning large quantities of coal and oil and by cutting down forests. In 1850, there were 280 parts per million of carbon dioxide (二氧化碳) in the atmosphere. Now there are 360, and this figure is expected to rise to 460 by the year 2030. We now put 24 billion metric (公制的) tons of carbon dioxide into the atmosphere every year. We have also created a group of artificial greenhouse gases that are 20,000 times more effective than carbon dioxide in trapping heat in the atmosphere. These are the chlorofluorocarbon (氟氯碳) gases, which are used in refrigerators and air conditioning systems.
The rapid increase in greenhouse gases is making the world warmer. The world's temperature has already gone up by half a degree this century, and the sea level has risen by ten centimeters. If the amount of carbon dioxide in the atmosphere doubles, there will probably be a rise in the earth's temperature of between 1° and 4°. This may seem a small increase, but it would be enough to cause major changes in geography and agriculture. Large areas of the world would be flooded, and some regions would become dry and unable to produce crops. It is important, too, to consider that there may be a delay of about thirty years in the greenhouse effect, This means that we are probably experiencing only now the effect of the gases put into the atmosphere up to the 1960s. Since then, our use of these gases has greatly increased.
According to the passage, a greenhouse is built to
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Earth's Inner Core
Scientists have long struggled to understand what lies at the planet's center. Direct observation of its center is impossible, so researchers must(51) to other evidence.
In 1889, a German scientist detected a severe earthquake in Japan. Geophysicists concluded that shock waves(52) jolts (晃动)from one side of Earth through the center to the other side. Then in 1936, Danish geophysicist lnge Lehmann studied the waves'(53) to determine that within Earth's core of molten (熔化了的)iron lies a solid inner core - but(54) that core was made of eluded (难倒)her. Other geophysicists quickly determined that Lehmann's inner core was composed mostly(55) iron. Since then, Lehmann's discovery has(56) conventional Earth science.
But now scientists are challenging traditional theory with new and radical(57) . For example, Earth's center could actually contain an "inner core within the inner core," claim Ishii and colleague Adam Dziewonski.
Analyzing hundreds of thousands of earthquake wave(58) , they maintain that the inner core has at its heart a tiny, even more solid sphere (球体). This sphere "may be the oldest fossil(59) from the formation of Earth," says Dziewonski.
Dziewonski and Ishii speculate that shortly(60) Earth formed around 4.8 billion years ago, a giant asteroid (小行星)smashed into the young planet and nearly melted it. But Earth's center didn't quite melt; it(61) mass as the planet cooled. The core within a core may be the kernel (核心)that endured. "its presence could change our basic ideas about the(62) of the planet," Dziewonski says.
Dziewonski's idea is tame (温和的)compared to the(63) theories of independent geophysicist J. Marvin Herndon. Earth's inner core is made not of iron, he claims, but a(64) of nickel and silicon. Herndon has a truly revolutionary notion: Within the nickel silicide (硅化物)inner core is also an "inner" inner core - an 8 km-wide ball of the element uranium. Uranium is radioactive. Herndon thinks the uranium releases heat energy as its atoms(65) fission-split and crash into one another in a chain reaction. In other words, we may live on top of a gigantic, "natural" nuclear power plant.
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Laughter
There is an old saying in English: "Laughter is the best medicine". Until recently, few people took the saying very seriously. Now, however, doctors have begun to investigate laughter and the effects it has on the human body. They have found evidence that laughter really can improve people's health.
Tests were carried out to study the effects of laughter on the body. People watched funny films, while doctors checked their heart rate, blood pressure, breathing and muscies. It was found that laughter has similar effects to physical exercise. It increases blood pressure, the heart rate and the rate of breathing; it also works several groups of muscles in the face, the stomach, and even the feet. If laughter exercises the body, it must be beneficial.
Other tests have shown that laughter appears to be capable of reducing the effect of pain on the body. In one experiment doctors produced pain in groups of students who listened to different radio programs. The group which tolerated the pain for the longest time was the group which listened to a funny program. The reason why laughter can reduce pain seems to be that it helps to produce endorphins (内啡肽) in the brain. These are natural chemicals which diminish both stress and pain.
There is also some evidence to suggest that laughter helps the body's immune system, that is, the system which fights infection. In an experiment, one group of students watched a funny video while another group served as the control group-in other words, a group with which to compare the first group. Doctors checked the blood of the students in both groups and found that the people in the group that watched the video had an increase in the activity of their white blood cells, that is, the cells which fight infection.
As a result of these discoveries, some doctors and psychiatrists (精神病学家) in the United States now hold laughter clinics, in which they try to improve their patients' condition by encouraging them to laugh. They have found that even if their patients do not really feel like laughing, making them smile is enough to produce beneficial effects similar to those caused by laughter.
We learn from the first paragraph that laughter
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